Those standard vert feeds on older markers only fit loaders with the standard thing one piece feedneck these include:
Grav Fed loaders, Eggys, Viewloader Revy, Rotor, and some other viewloader loaders. The Tippmann SSL-200 also works. That's all I can think of off the top of my head. Loaders with reinforced shells will NOT fit: Invert Halo TOO, Reloader B or Magna, & Empire Prophecy.